Anyone who pays attention to temperatures around Washington and Baltimore knows that it is much warmer in these cities than in the surrounding suburbs, especially at night. This is due to a phenomenon known as the urban heat island effect. Essentially, all of the asphalt and concrete in the urban core traps heat near the ground, creating a zone of elevated temperatures.

But these urban heat islands are not uniform. Some neighborhoods have more dark, heat-absorbing surfaces and are particularly hot. As a result, they suffer the most during the summer’s punishing heat and are most vulnerable to health effects. From July 17 to July 20, the National Oceanic and Atmospheric Administration (NOAA) is leading a field campaign involving citizen volunteers to map and better understand the Washington and Baltimore heat islands.

The volunteers will “fan out across these cities in cars equipped with special thermometers designed to measure air temperature once per second as well as record the time and precise location of each measurement,” NOAA’s description of the campaign says. “Thus, the data collected by the teams of volunteer drivers will enable the scientists to generate very detailed maps of temperatures across both cities at three different times of day: 6:00 am, 3:00 pm, and 7:00 pm.”

NOAA has already received more than enough volunteers to conduct the campaign.

Once the campaign is completed and the data processed, NOAA plans to publish the findings in scientific journals and make the data publicly available. The detailed maps, which will reveal which specific areas are the hottest, could help officials better identify which communities need the most help during heat waves. They could also guide city planners in efforts to cool the heat island by planting trees, removing pavement, and installing reflective and green roofs that absorb less heat.

The D.C. Policy Center produced one of the first detailed analyses of the D.C. heat island last summer using data from NASA’s LandSat 8 satellite. NOAA’s effort this summer will be the first using direct measurements.

Similar to what’s planned for Washington and Baltimore, NOAA conducted an investigation of Richmond’s heat island last summer, working with partners at the Science Museum of Virginia and Portland State University. It recruited volunteers from several local organizations, which made up 15 teams that spread out around the city on cars and bikes to take temperatures at different times and locations.

Researchers at Portland State University crunched the data and produced a map.

“The map showed differences of up to 16 degrees across Richmond’s neighborhoods during the hottest part of the day,” noted NOAA’s case study on the project. “This means that when a heavily shaded neighborhood in Richmond experiences an afternoon temperature of 87 degrees, it might reach 103 degrees in a more urbanized neighborhood in the same city. The data also revealed that warmer areas experienced a greater difference between morning and afternoon temperatures than did cooler areas.”

NOAA’s case study added that the maps and data are being used to inform an update to Richmond’s citywide master plan and several other climate planning initiatives.

The researchers at Portland State University are working toward developing an “off the shelf” system that communities across the country can use to evaluate temperature differences within a city and their implications. It involves taking the detailed heat island maps and overlaying demographic, air pollution and landscape information to help local governments identify the particular areas most vulnerable to heat.

“With climate change, we expect summer heat waves to become longer and more intense and frequent,” said Vivek Shandas, research director for Portland State’s Institute for Sustainable Solutions. “By identifying characteristics of neighborhoods and households that are the most vulnerable, we can reduce the health impacts of intense heat waves nationally.”